Sensitized, photo-sensitive glass and its production

ABSTRACT

A sensitized, photo-structurable glasses and methods for producing are provided. The glasses includes Si 4+ , one or more crystal-agonist, one or more crystal-antagonist, and one or more pair of nucleating agents. The glasses are sensitized in that the glass reacts more sensitive to irradiation with UV-light and can be crystallized easier and with higher aspect ratios than a non-sensitized glass with equal composition. Furthermore, the sensitized glasses of this invention have smaller crystal sizes after irradiation and tempering than a non-sensitized glass with equal composition. The invention also relates to a structured glass product. Such product can be obtained by submitting the crystallized glass product to a subsequent etching step. The structured product can be used in components or as component for the application fields micro-technology, micro-reaction-technology, electronic packaging, micro-fluidics, FED spacer, bio-technology, interposer, and/or three-dimensional structured antennae.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims benefit under 35 U.S.C. §119(a) of German PatentApplication No. 102015107777.9 filed on May 18, 2015, of German PatentApplication No. 102015107778.7 filed on May 18, 2015, and of GermanPatent Application No. 102016101996.8 filed Feb. 4, 2016, the entirecontents of all of which are incorporated herein by reference

BACKGROUND

1. Field of the Invention

This invention relates to a photo-sensitive glass and to a process forits production. The glass of the invention is sensitized, that means itreacts more sensitive to irradiation with UV-light and can becrystallized easier and with higher aspect ratios than a non-sensitizedglass with equal composition. Furthermore, the sensitized glasses ofthis invention have smaller crystal sizes after irradiation andtempering than a non-sensitized glass with equal composition.

2. Description of Related Art

Photo-sensitive glasses are usually used for producing micro-structuredbodies. Thereby initially a glass is produced, which is photo-sensitive.This photo-sensitive glass is irradiated with UV-light on definedpositions. Subsequently, the irradiated areas, in which nuclei haveformed due to irradiation, are transformed by tempering into areas witha crystalline phase, which better dissolves in an etching medium thanthe non-crystallized glass. Consequently, the thus processed bodies canbe selectively etched with an etching solution, which normally compriseshydrofluoric acid. The light exposed areas are etched by the etchingsolution in the range of 20 to 50 times faster than the intact glass.The result is a structured body.

Photo-sensitive glasses are known from the prior art for a long time.

The photo-structurable glass described in document US 2011/0195360 A1comprises comparably much boron, aluminum and potassium as well aslittle silicon. The amount of alkali metal oxides is very high in theglasses described therein, apparently for reducing the melting point,which is increased due to the high aluminum content. In combination withthe low content of silicon dioxide this results in a compromisedchemical resistance. Accordingly, a high proportion of zinc oxide isused for improving the chemical resistance. The composition of the glassis not precisely described in this prior art document; the specifiedranges are very wide and do not allow any conclusion with regard to theexact proportions. Also the process of production of the glass is notdescribed. The glass is not sensitized, it thus has not the coolingstate of the glasses of this invention.

Also U.S. Pat. No. 2,971,853 describes photo-structurable glasses thatare supposed to be completely light exposed and ceramized. It is aimedat transforming the formed metasilicate crystals in the direction of thedisilicate stoichiometry—thus towards lower alkali metal contents—byfurther temperature treatment. Accordingly, the contents of sodium andpotassium are very low in the glass described therein. Furthermore, theimportance of boron and zinc for the glass composition was notrecognized in the document. The glasses were melted under differentredox-conditions, however only in laboratory scale (1 pound).Furthermore, the glasses described in the document are not determinedfor structuring but they are supposed to be completely ceramized afterirradiation. Thus, a ceramic body is produced and not a structured glassbody.

DE 10 2005 003 595 A1 describes optical elements and systems, whichcomprise photo-sensitive glass or photo-sensitive glass ceramic. Theglasses may be oxidic glasses or chalcogenide glasses. The compositionalranges do not allow any conclusion with regard to specific compositions.Differences in refractive index are supposed to be induced byirradiation. The glasses are not supposed to contain any antimony. Othercrystal stoichiometries are aimed at as compared to the presentinvention. The glasses may be melted under oxidizing conditions.However, there is no processing in the sense of a sensitization afterthe melt so that a high cooling state of the glasses has to be assumed.Apart from that, the glasses described therein contain very much sodiumand halides and little lithium. The production of glass bodies is donevia cutting and polishing of a bulk glass.

DE 10 2008 002 104 A1 describes a glass that has a crystal phase ofspodumene or lithium disilicate. The glass is supposed to have acoefficient of thermal expansion, which is as low as possible. Thecomposition described therein has relatively much zinc and aluminum andonly a little amount of sodium. DE 1 696 473 describes a process forproducing crystalline mixed-bodies. The underlying glass contains verymuch aluminum and zinc. DE 103 04 382 A1 relates to a photo-structurablebody. The glass underlying the body contains high amounts of aluminum.Furthermore, the glasses contain only little nuclei source in relationto cerium. US 2008/0248250 A1 relates to a process for production ofstructured glass structures with a high an anisotropic etching rateratio. The glasses described therein contain relatively little silicon,in total a lot of sodium and potassium, a lot aluminum and a lot ofboron.

All prior art documents have in common that the described glasses are ina high cooling state, thus have not been subjected to any sensitization.None of the documents suggests cooling the glasses slowly after the meltor subjecting the glasses to a controlled cooling step (sensitization)in a separate processing step after the melt. This would eventually alsobe against the experience of the skilled person that aims at a fastpassage through the crystallization range (quenching) of such acrystallization-sensitive glass. As far as an increased crystallizationtendency was aimed at in the prior art, this was tried to be achieved byadaptation of the compositional ranges, in particular of the nucleatingagents. Improving the structurability by reducing the cooling state hasnot been suggested by the prior art.

SUMMARY

It has to be differentiated between unwanted crystallization in glassproduction, which is also called “devitrification”, and directedcrystallization, which can be achieved in photo-structurable glasses bylight exposure and tempering. It is indeed a crystallization process ineach case, however, the processes differ with regard to the occurringcrystals. While alkali disilicates are formed in devitrification, alkalimetasilicate crystals are generated in directed crystallization inphoto-structurable glasses. Despite the described differences withregard to the processes underlying crystallization, photo-structurableglasses also have an increased tendency to devitrification in additionto the tendency to crystal formation induced by exposure to light andtempering desired for photo-structurability.

Consequently, producing such glasses in good quality and withoutunwanted crystallization is not trivial. The crystallization tendency ofthe glasses is at least in part based on the presence of a pair ofnucleating agents. In the prior art, for this purpose the pair ceriumand silver is used amongst others. The chemical process underlying theformation of nuclei is described by the following reaction equation:

Ce³⁺+Ag⁺ +hv→Ce⁴⁺+Ag⁰  (Equation 1)

Upon irradiation of photo-sensitive glasses with UV-light at awavelength of about 320 nm, trivalent cerium yields an electron to thesilver ion, whereby elemental silver is generated. In a subsequenttempering step the desired crystal nuclei are formed around thegenerated atomic silver.

It is a challenge for producers of photo-sensitive glass to adjust agood balance between the desired crystallizability after production andthe critical crystallization tendency, which complicates the production.For example, increase of the applied amount of silver results information of elemental silver already during melting. This precipitatesand may result in silver bubbles or silver droplets, whereby theproduction is complicated or even becomes impossible.

Furthermore, production is also particularly challenging for the reasonthat the components cerium and silver, respectively, have to be presentin the correct oxidation state in the final glass so that the reactionas described above (Equation 1) can take place. Of course, an oxidizingmelting procedure results in prevention of precipitation of colloidalsilver because reduction to metallic silver does not occur. However, insuch a case, cerium is present in its tetravalent form in the glass sothat the desired reaction (Equation 1) cannot take place upon exposureto UV-light.

On the other hand, if a reducing melting procedure is selected, forincreasing the amount of trivalent cerium, the risk is increased thatsilver nuclei are formed already during production. Silver nuclei inunexposed glass disturb selective crystallization of the glass bytempering because also unexposed areas would crystallize. Moreover, theglass would not fulfill the transmittance requirements. Rather, it isdesired that no silver nuclei are formed during production so thatessentially the entire silver in the glass is available as monovalentsilver ions for reaction of Equation 1.

It is discussed intensively in the literature, how the melting procedurecan be optimized for maximizing the photo-sensitivity of the obtainedglass without compromising the processability of the glass. This goalwas not satisfyingly achieved so far.

Thus, there is still no photo-sensitive glass available that could forexample be processed in continuous production methods or hot processingmethods (down draw, new down draw, overflow fusion, pressing,redrawing). It is therefore an object of the present invention toprovide a glass that is suitable for continuous production and forprocessing in modern glass processing methods without having inferiorproperties with regard to crystallizability and photo-sensitivity ascompared to the glasses of the prior art. In contrast, the glasses ofthe present invention are preferably even better than the prior artglasses with respect to crystallizability, aspect ratio and etching rateratio.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the cooling curve of glass B1.

FIG. 2 shows a cooling curve with logarithmically plotted x-axis.

FIG. 3 shows the influence of sensitization of an example glass on thetransmittance in the UV-region.

FIG. 4 shows transmittance of an example glass with a thickness of 1 mmin dependence from the wavelength.

FIG. 5 shows the dependence of the achieved etching ratio from thetempering temperature.

FIG. 6 shows the standard deviation of the obtained hole-diameter independence from the designed hole-diameter.

DETAILED DESCRIPTION

The object of this invention is solved by a sensitized,photo-structurable glass that comprises Si⁴⁺, one or morecrystal-agonist, one or more crystal-antagonist and one or more pair ofnucleating agents, wherein the crystal-agonists are selected from Na⁺,K⁺, and Li⁺, wherein the crystal-antagonists are selected from Al³⁺,B³⁺, Zn²⁺, Sn²⁺ and Sb³⁺, wherein the pair of nucleating agentscomprises cerium and at least one agent from the group of silver, goldand copper, wherein the molar proportion of the crystal-agonists incat.-% in relation to the molar proportion of Si⁴⁺ is at least 0.3 andat most 0.85 and the glass has a cooling state that corresponds to asteady cooling from a temperature T1 to a temperature T2 with a coolingrate K of at most 200° C./h, wherein temperature T1 is at least abovethe glass transition temperature T_(g) of the glass and temperature T2is at least 150° C. below T1. In a particular preferred embodiment, T1is 100° C. above the glass transition temperature T_(g) of the glass andtemperature T2 is 250° C. below T1. In another preferred embodiment, T1is 50° C. above the glass transition temperature T_(g) of the glass andtemperature T2 is 200° C. below T1. In another preferred embodiment, T1is 25° C. above the glass transition temperature T_(g) of the glass andtemperature T2 is 150° C. below T1. “Steady” means in this context thatit is cooled down continuously from T1 to T2 without the glass beingkept on certain temperature levels. In particular, cooling withessentially constant cooling rate is meant therewith. Preferably,maximum and minimum cooling rate during cooling from the temperature T1to the temperature T2 deviate from the average cooling rate K by at most±20%, more preferably by at most ±15%, more preferably by at most ±10%,more preferably by at most ±5%, respectively. As far as it is cooled toroom temperature after cooling to T2, also this further cooling canoccur steadily, but further cooling below T2 is not decisive. Roomtemperature is preferably 20° C. It was surprisingly found that theadjustment of the cooling state in accordance with the invention makesthe glass more susceptible for crystallization even if melting was donein a relatively oxidizing way.

The cooling state of a glass can be determined on a given glass alsowithout knowledge of the manufacturing conditions. For determining thecooling state of a glass sample P, initially its refractive index n_(d)and/or its mass density p are determined. The sample is then preferablydivided into several individual samples P1, P2, P3 and so on. Eachsample is then heated to temperature T1 and subsequently cooled down totemperature T2 with different cooling rate K1, K2, K3 and so on. Aftercooling to temperature T2 and preferably further cooling to roomtemperature, index of refraction n_(d) and/or mass density p aredetermined again so that each of the values can be assigned to a coolingrate. The obtained pairs of values can then be plotted in a coordinatesystem, wherein the ordinate represents the optical density and theabscissa represents the cooling rate. Based on the so obtained coolingcurve a conclusion can be drawn from the density of the glass sample Pto the cooling state thereof. An example is shown in FIG. 1. It can beseen that the index of refraction decreases with increasing coolingrate. Thus, a quenched glass has a lower index of refraction than aslowly cooled glass. In case the x-axis is plotted logarithmically, thecorrelation arises from a simple linear equation. An example thereof isshown in FIG. 2.

The terms refractive index and index of refraction are used synonymouslyin the present description.

The cooling state of a glass is thus a measure for the conditions duringthe cooling of the glass. A conventionally “quenched” glass, which wascooled very fast from the melt (for example >>300° C./h), has a highcooling state. The ions in such a glass are “frozen” in a comparablydisordered state. So to speak, by fast cooling from the melt, the glassis thus “frozen” on a high energy level. The high temperature ranges, inwhich a spatial approaching of the crystal components (crystal-agonists,Si⁴⁺) was still possible due to low viscosity, was passed through fast.Therefore, a fast cooled glass, which is on a high cooling state, has acomparably low density or index of refraction. The differences of theindex of refraction of a glass in dependence from its cooling state arecomparably low. However, because these properties can be measuredreliably up to the sixth decimal place and beyond, this method isnevertheless suitable for providing a reliable measuring result.Experiments have shown that the sensitizing of glass as described hereincauses an increase in refractive index at least in the fifth, preferablyeven in the fourth decimal place.

The cooling state according to the present invention preferably ensuesif the glasses of this invention are subjected to a sensitization stepas described herein. This sensitization step is described further below.If herein a sensitization step is mentioned, this always means atreatment step, which occurs prior to light exposure of the glass. Theheat treatment step after light exposure of the glass is herein called“tempering” in accordance with the literature.

The inventors think that it is probable that for the bettercrystallizability of glasses sensitized according to the presentinvention there are a plurality of reasons, which result from thecomplex interplay of glass composition and sensitization or productionmethod. Thereby it is probable that an approaching of the crystalcomponents is reached by the sensitization. This approaching could beenabled by the glass being in a viscosity range, which allows diffusionof the crystal-agonists in the network, for a comparably long time span(in comparison to cooling by quenching) during cooling from T1 to T2.Thereby the glass approaches the crystalline state, however, withoutcrystallizing. So to speak, it is more sensitive for the desiredcrystallization after a UV-exposure.

In addition, a sensitized glass has a more close-meshed glass structuredue to its higher density. This could be the reason for the particularlysmall crystals forming in the crystallized glass. Finally,crystal-agonists, whose mobility is important for crystallization,cannot as easily move by diffusion in a close-meshed structure as in acomparable coarser network. Thereby crystal growth should be hindered inthe sensitized glass so that crystals may indeed be formed around thegenerated nuclei, however, their growth and thus the association ofseveral crystals to larger crystals is hindered. The result are finecrystal arrangements that allow etching of particularly fine structures.

Furthermore, it turned out that due to the sensitization theself-absorption of the glass matrix (band edge) in the importantUV-region around the absorption maximum of Ce³⁺ is shifted in thedirection of smaller wave-lengths. Thereby the absorption in this regionis overall smaller and the UV-light, which is used for irradiation, canenter deeper into the glass and can achieve a deeper structure depth.The results shown in FIG. 3 prove the increase in transmittance in theUV-region achieved by sensitization.

In accordance with the invention is thus a glass having a cooling state,which corresponds to a comparably low cooling rate. Prior art glassesare cooled with very high cooling rate for keeping the crystallizationrisk down. In contrast, the glasses of the invention have been cooled bythe sensitization in such a way, either directly from the melt or in asubsequent step following the melt and if applicable following hotforming, that a cooling state of at most 200° C./h is reached.Preferably, the cooling state is even below 150° C./h, more preferablybelow 120° C./h, more preferably below 100° C./h or below 85° C./h. In apreferred embodiment, the cooling state can even be below 80° C./h. Inevery given glass the cooling rate can be correlated with the refractiveindex as shown in FIG. 1 and an unambiguous relation can be established.However, the glass of the invention cannot simply be characterized byindication of the refractive index because the glass composition has amuch greater impact on the refractive index than the cooling rate.

However, it has to be considered that due to the circumstances describedabove (ion mobility, crystal formation)—dependent on the glasscomposition—a certain cooling state should not be undercut. At a veryslow cooling, the glass may stay in a temperature range, which enablescrystal formation, for too long. Then crystallization would occur. Itturned out to be advantageous, not to undercut a cooling state of 10°C./h, more preferably 20° C./h, particularly preferably 40° C./h andmore preferably 60° C./h for not risking crystallization. This does notexclude that certain glass compositions tolerate even such a low coolingstate.

The term “cooling state of X° C./h” indicates a cooling state thatcorresponds to a cooling from a temperature T1 to a temperature T2 witha steady cooling rate K of at most X° C./h. It has to be noted that theindication of a “cooling state that corresponds to a cooling from atemperature T1 to a temperature T2 with a steady cooling rate K of atmost X° C./h” does not mean that the so characterized glass wasnecessarily cooled with such a steady cooling rate from T1 to T2.Rather, it is meant that it has the same cooling state as such a glass.The glass of the invention could also have been cooled from atemperature T1 with a cooling rate K′ to a temperature T1′ and then witha cooling rate K″ to a temperature T2. Crucial is the obtained coolingstate, which is indicated for ensuring clarity and measurability.

In the glass of the present invention, alkali metasilicate crystals areformed upon tempering after light exposure. Metasilicates arecharacterized by a stoichiometry, which has one mole crystal-agonists,for example an alkali metal oxide as Li₂O or Na₂O, per mole of silicondioxide (SiO₂). Thus, the stoichiometric ratio of alkali metal ions tosilicon ions in the metasilicate is 2:1. If both components, alkalimetal oxide and silicon dioxide, in this stoichiometric ratio of thecrystal were together melted and cooled down, no glass would be formedbut a ceramic.

In order to obtain a glass and not a ceramic, according to the inventionon the one hand the glass composition substantially deviates from thiscrystal stoichiometry and on the other hand crystal-antagonists are usedfor decreasing the crystallization tendency of the glasses.

According to the invention, “glass” is understood as an essentiallyamorphous material and “ceramic” as an essentially completelycrystalline material. A material that contains both crystalline andamorphous phases is called “glass-ceramic”.

It turned out to be advantageous to select the stoichiometry ofcrystal-agonists and silicon in form of Si⁴⁺ in such a way that themolar ratio in cat.-% of crystal-agonists to Si⁴⁺ in the glass is atleast 0.3, more preferably at least 0.5 and further preferably at least0.55. However, this ratio should preferably not exceed a value of 0.85,more preferably of 0.7, particularly preferable is a ratio of at most0.65. If namely with respect to Si⁴⁺ a too low amount ofcrystal-agonists is used, then the composition departs too far from thedesired stoichiometry and the crystallization tendency is stronglyreduced. Crystallizing such a glass would be lengthy andenergy-intensive. Furthermore, mostly disilicates would be formed, whichdo not show such a substantial solubility difference in comparison toglass with regard to common etching solutions as the desiredmetasilicates. A too high amount of crystal-agonists, however, wouldincrease the crystallization tendency strongly due to approaching thestoichiometry of the metasilicate and would complicate or makeimpossible the processability.

A glass melt has a very high temperature, which is well abovetemperature ranges, in which crystals or nuclei may form. For example,the glass of the invention is melted at temperatures that are preferablyabove 1300° C., more preferably above 1400° C. Such a temperatureassures that all components are melted. Preferably, a temperature of1800° C., more preferably 1700° C. and particularly preferably 1600° C.should however not be exceeded because too high temperatures favor thereduction of silver in the glass and additionally the energy demand isthereby strongly increased. Only upon cooling of the glass melt afterthe production, the crystallization tendency increases until theviscosity of the melt is so high that no more nuclei can be formed. Thereason is that diffusion of crystal components is restricted withincreasing viscosity. Thus, there is a temperature range that isassociated with particularly pronounced crystallization tendency. Forthe glass of the present invention this is in the range of from 990° C.to 600° C., in particular to 460° C. For this reason,crystallization-susceptible glasses have to be cooled fast enoughthrough this range. When it is cooled too slowly, the thermodynamicallypreferred crystal phase is formed and no glass is obtained, but aglass-ceramic. This mostly applies also to the glass of the presentinvention with the exception that in accordance with the presentinvention a sensitization takes place, either by cooling the melt in thetemperature range from T1 to T2 comparably slowly or by initial fastcooling from the melt and then a slow cooling from T1 to T2 in asubsequent sensitization step.

By fast cooling the glass is so to say “frozen” on a high energy level.Just due to the high viscosity of the glass it is not transformed intothe energetically more favorable crystal state. This is also the reasonwhy photo-sensitive glasses are tempered after irradiation. Otherwise,neither the temperature necessary for nuclei formation (“nuclei formingtemperature”) would be achieved in the irradiated photo-sensitiveglasses nor the higher “crystal growth temperature”. Both temperaturesrepresent temperature ranges. The prior irradiation ensures that in thetempering step crystallization of specifically the irradiated areas canbe achieved. Thereby in interaction with the higher etchability of thecrystallized areas, directed introduction of structures in thesubsequent etching step is enabled.

Glasses, which already have an extremely high devitrification tendencydue to their composition or due to the process management, have to becooled down from the melt very fast. Thereby the viscosity of the meltincreases so fast that no crystallization occurs. A glass is obtained,which is “frozen” on a high cooling state. Such a glass may be wellsuitable for photo-structuring due to the correlation betweendevitrification tendency and the tendency to crystal formation inducedby light exposure and tempering as described above. The desired crystalsare formed fast upon tempering after light exposure. However, such aglass can be post-processed only with relatively cost-intensiveprocesses. A priori most processes are excluded, in which the glass hasto be re-warmed. Eventually in re-warming nothing else happens than intempering: diffusion of ions, in particular of small alkali metal ions,increases and nuclei and crystals are formed. Consequently, suchglasses, which inherently are particularly devitrification-susceptible,can only be post-processed coldly. A hot post-processing (for exampleredrawing) is out of question. The same applies for hot forming stepsdirectly from the melt (for example pressing, floating, rolling,out-rolling, down draw, overflow fusion). Glasses with such extremelyhigh devitrification tendency are not subject of the present invention.

The present invention provides glasses, which indeed have a pronouncedcrystallization tendency so that they can be photo-structured, whichhowever do not show extremely high devitrification tendency. This isachieved by the process management and/or by the composition of theglasses. For instance, the glasses of the invention significantlydeviate from the metasilicate stoichiometry, furthermore they arepreferably melted in a comparably oxidizing way.

Thereby it is achieved that the pair of nucleating agents (for examplecerium and silver) present in the glass is present with regard to thenuclei-source (in particular Ag) mostly in higher oxidation states.Thereby also a higher proportion of cerium will be present in theoxidation state Ce⁴⁺ than would be the case in a more reducing melt. Inthe prior art this constellation is mostly described as undesiredbecause as much Ce³⁺ must be present as possible for nuclei formationaccording to the reaction described above (Equation 1). However,according to the invention this is wanted for conferring the glass witha low crystallization tendency directly after the melt. According to theinvention, only later—after the melting but prior to the lightexposure—the ratio of Ce³⁺ to Ce⁴⁺ is shifted more towards Ce³⁺ by thesensitization. The ratio of both oxidation states of cerium canunfortunately not be determined in the glass. Namely, decomposition ofthe glass is changing the oxidation state and the transmittance bands ofCe⁴⁺ are in a wavelength region, in which the glass itself is stronglyabsorbing.

A preferred comparably oxidizing melting procedure has the advantagethat the glasses of this invention may be subjected to one or more hotprocessing steps directly after the melt or at a later time point, inany case however prior to light exposure and in particular also prior tosensitization. The pair of nucleating agents is so to say restricted inits activity at the time point of hot processing due to the presence ofCe⁴⁺. However, without nuclei no crystals are formed. The glass or themelt are thus in a comparably uncritical state with regard tocrystallization.

Suitable hot processing steps in accordance with the invention are forexample pressing, down draw, new down draw and redrawing. These hotprocessing methods are well known from the prior art. They can beperformed as known with the glass of the invention, however with theproviso that the melt should be cooled relatively fast through thetemperature range from 990° C. to 600° C., in particular to 460° C. T1is preferably below 600° C. so that a fast passing through the indicatedtemperature range preferably allows for a directly subsequentsensitization. In the temperature range from 990° C. to 600° C. thecrystallization risk is substantial even for the glass of the invention.The indicated temperature range should therefore be passed through innot more than 120 minutes, more preferably not more than 60 minutes,more preferably not more than 30 minutes and particularly preferably notmore than 15 minutes. In particularly preferred processes, the indicatedtemperature range is preferably even passed through in less than 5minutes, in particular less than 2 minutes.

A crucial aspect, which is responsible for the substantial but moderatecrystallization tendency of the present glasses, is their composition.This invention is based to a large degree on the correct adjustment ofthe molar ratios of the cations to each other (crystal stoichiometry).Therefore, it is reasonable to characterize the glass composition byindications in cat.-%. Of course the glass also comprises anions, whichshall also be described below. However, they are less formative for theproperties of the glass than the cations so that the core of theinvention is more in the cation composition.

The term “cation percent” (abbreviated “cat.-%”) relates to the relativemolar proportions of the cations with regard to the total amount ofcations in the glass. Of course the glass also comprises anions, whoserelative molar proportions in relation to the total amount of anions inthe glass is herein indicated as “anion percent” (abbreviated“anion-%”).

As described at the beginning, the glass of the invention comprises Si⁴⁺in any case. This component is added to the melt preferably in form ofSiO₂ (sand). Si⁴⁺ is crucial for the glass properties and for thecrystallization behavior because it is a key component of the alkalimetasilicate crystal. The stoichiometry of the alkali metasilicatecrystal is shown subsequently:

R₂O₃Si R=alkali metal ion

In a preferred embodiment the glass of the invention comprises silicon(Si⁴⁺) in an amount of at least 45 cat.-%, further preferred at least 50cat.-%, more preferred at least 52 cat.-% and particularly preferred atleast 56 cat.-%. The content of this component should not exceed a valueof at most 65 cat.-%, further preferred at most 63 cat.-%, furtherpreferred at most 61 cat.-% and particularly preferred at most 60.5cat.-%. The amount of this component has to be considered because a toolow amount of silicon can impair the crystallization tendency toostrongly. Very small amounts of silicon would even result an increase ofcrystallization tendency in such a way that no glass is obtained at all.Furthermore, silicon is an important glass former, which criticallyco-determines the glass network. If however too much silicon is added,the glass network becomes denser. This restricts the ion mobility in theglass and prevents the diffusion in particular of alkali metal ions sothat crystal formation would be prevented.

The selection of the right amount of silicon is comparably complexbecause not only the proportion of silicon is alone decisive but alsothe proportions of Al³⁺ and B³⁺ as well as the ratio of alkali metalions to silicon play a role. According to the invention, the molar ratioof alkali metal ions to the molar proportion of silicon is at least 0.3to at most 0.85. Preferably, this ratio should be at least 0.4 and atmost 0.8, more preferably at least 0.5 and at most 0.75 and particularlypreferably at least 0.6 and at most 0.7.

Consequently, also the proportion of crystal-agonists in the glass playsa role. According to the invention, the crystal-agonists are preferablyselected from the cations of lithium (Li⁺), sodium (Na⁺) and potassium(K⁺). Preferably, the glass of the invention contains all threecomponents Li⁺, Na⁺ and K. The total amount of these components shouldpreferably be at least 30 cat.-%, further preferably at least 32 cat.-%and more preferably at least 34 cat.-%. However, an amount of 45 cat.-%,further preferred 43 cat.-%, more preferred 40 cat.-% or 38 cat.-%should not be exceeded. A too large amount of these components would onthe one hand very strongly increase the crystallization tendency of theglass and would on the other hand strongly reduce the chemicalresistance of the glass. At a too low amount of these components thecrystallization tendency would be strongly reduced because this wouldinherently result in a larger deviation from the metasilicatestoichiometry.

However, not only the total amount of crystal-agonists is relevant butalso the content of the respective individual components and theirratios to each other. The glass of the invention preferably compriseslithium in an amount, which exceeds the molar amounts of each of sodiumand potassium. Preferably, the content of lithium also exceeds thecontent of the sum of potassium and sodium in the glass. With otherwords, preferably lithium is the main component among thecrystal-agonists. The amount of lithium in the glass of the invention ispreferably at least 20 cat.-%, further preferably at least 25 cat.-%,more preferably at least 27.5 cat.-% and particularly preferably atleast 28 cat.-%. The content should preferably be at most 40 cat.-%,further preferably at most 35 cat.-% and particularly preferably at most32 cat.-%. The ratio of lithium to silicon should preferably be at least0.4 and more preferred at least 0.45. In particular, this value is atmost 0.7, further preferably at most 0.65, more preferably at most 0.6and particularly preferably at most 0.55.

Because lithium is preferably the main component among thecrystal-agonists, with regard to advantages and disadvantages of theindicated ratios of lithium to silicon the same applies as describedabove for the ratio of crystal-agonists to silicon. Lithium ispreferably the main component among the crystal-agonists according tothe invention because lithium is particularly mobile since it is thesmallest cation of the alkali metals. This facilitates diffusion oflithium in comparison to the other alkali metals and enablessensitization of the glass at comparably low temperatures and comparablyfast.

Indeed lithium is preferably the main component of the crystal-agonistsin the glass of the invention and thus exceeds with regard to the molarproportion the proportions of the components sodium and potassium.Nevertheless, the glass of the invention preferably also contains thecomponents potassium and/or sodium in addition to lithium. Thereby it ispreferred that the component potassium exceeds the component sodium inits molar proportion. It has turned out that thereby the tendency of theglass to build the desired metasilicate crystals after light exposure isincreased. A too high amount of sodium in relation to potassium wouldfavor crystal formation in favor of the disilicates. Potassium mayimprove the chemical resistance of the glass when used in small amounts.Furthermore, potassium reduces the devitrification tendency of the glassat the production. The content of potassium in the glass of theinvention should preferably be at least 2 cat.-%, further preferably atleast 2.5 cat.-%, more preferably at least 3 cat.-% and particularlypreferably at least 3.5 cat.-%. However, the content of this componentshould preferably be at most 8 cat.-%, further preferably at most 7cat.-%, more preferably at most 6 cat.-% and particularly preferably atmost 5 cat.-%.

According to the invention, the component sodium should preferably bepresent in a proportion of at least 1 cat.-%, further preferably atleast 1.5 cat.-%, more preferably at least 2 cat.-% in the glass.Preferably, a content of at most 5 cat.-%, further preferably at most 4cat.-% should not be exceeded. In a particularly preferred embodiment,the content of sodium in the glass does not exceed a value of 3 cat.-%.This ensures that the formation of disilicates is mostly prevented.

As mentioned in the beginning, the glasses of the invention do not onlycontain silicon and crystal-agonists but also at least one agent fromthe group of crystal-antagonists. According to the invention, preferredcrystal-antagonists are aluminum (Al³⁺), boron (B³⁺) and zinc (Zn²⁺) aswell as tin (Sn²⁺) and/or antimony (Sb³⁺). The crystal-antagonists servefor inhibiting formation of crystals or nuclei. If nocrystal-antagonists were added, the glass would crystallize very fast.Potentially, no glass would be obtained at all. According to the presentinvention, the content of the crystal-antagonists should preferably beat least 2 cat.-%, more preferably at least 2.5 cat.-%, particularlypreferably at least 3.5 cat.-%. For not inhibiting crystal formation toomuch, the content of the crystal-antagonists is preferably restricted toat most 9 cat.-%, further preferred are at most 8 cat.-% and morepreferably at most 7.5 cat.-%. In particularly preferred embodiments,the content is restricted to at most 5.5 cat.-%.

Among the crystal-antagonists aluminum is preferably the main component,which means that the component aluminum is present in the glass withregard to the molar amounts in a higher proportion than the remainingcrystal-antagonists, in particular than the components boron and zinc.This has the advantage that aluminum does not hinder the formation ofmetasilicates when it is used in limited amounts. For this purpose,according to the present invention preferably at least 2 cat.-%, morepreferably at least 3 cat.-% and particularly preferably at least 3.5cat.-% aluminum are used. Aluminum decreases the devitrificationsensitivity. However, the amount of aluminum used should also not be toohigh because this on the other hand could lead to formation of spodumenemixed crystals. Furthermore, aluminum increases the melting point of theglass, which has to be balanced by use of larger amounts of alkali ions.For this reason, the component aluminum should be used in amounts thatpreferably do not exceed 8 cat.-%, more preferably 7 cat.-%, furtherpreferably 6 cat.-% and particularly preferably 5 cat.-%. Inparticularly preferred embodiments, the amount of aluminum is restrictedto at most 4.5 cat.-%.

Because the recommendable amount of aluminum is restricted due to therisk of formation of other crystal phases, it may be necessary to usefurther crystal-antagonists. Thereby particularly boron and zinc comeinto consideration. The invention comprises both glasses, which containboron but no zinc, or zinc but no boron, as well as such glasses thatcomprise these both components in combination. Therein it is preferredthat the amount of boron is strongly restricted. Background is thatboron shows a very strong effect on crystallization tendency. If toomuch boron is used, the crystallization tendency is very much decreased.For this reason boron is preferably used in amounts that do not exceed 3cat.-%. Further preferably this component should not be used in amountsthat are larger than 1.5 cat.-% and particularly preferably not largerthan 0.5 cat.-%, in particular not larger than 0.35 cat.-%. A minimumamount of boron may however be advisable. According to the invention,this is preferably at least 0.05 cat.-%, further preferably at least 0.1cat.-% and particularly preferably 0.2 cat.-%.

Zinc can serve as crystal-antagonist additionally or alternatively toboron. If both zinc and boron are used, the amount of zinc should behigher than the amount of boron with regard to the molar proportions ofthe cations. Preferably, the amount of zinc is even at least 1.5 timesas high as the molar proportion of boron, however in particular nothigher than 2.5 times as high. In preferred embodiments the glasscomprises zinc in an amount of at least 0.2 cat.-%, further preferred atleast 0.3 cat.-% and particularly preferred at least 0.45 cat.-%. Zincprevents the undesired reduction of silver and thus the uncontrolledformation of nuclei by removal of terminal oxygen in the glass. However,if too much zinc is used, crystallization tendency decreases strongerthan desired. Therefore, the amount of zinc should be at most 2.5cat.-%, further preferred at most 1.5 cat.-% and particularly preferredat most 0.8 cat.-%.

In addition to the indicated components also antimony (Sb³⁺) and tin(Sn²⁺) may serve as crystal-antagonists. Tin and antimony serve asreducing agents, which provide for a particularly fine distribution ofthe nuclei-source in the glass. This effect occurs in particular at lowamounts of these components. For the component tin the proportion ispreferably below 0.1 cat.-%. Preferably, the glass is even free of tin.

The preferred amount of antimony in the glass is restricted to at most0.4 cat.-%, further preferably at most 0.2 cat.-%. The inventors foundout that the transmittance in the UV region is surprisingly increased atlow proportions of antimony in the glass. Thereby the UV-light, which isused for irradiation, can enter deeper into the glass so that a deeperstructure depth can be achieved. Thus, via the antimony-content also theextent of absorption in the UV-region and thereby the achievable depthof light exposure can be adapted independent of the cerium-content.Particularly preferably the proportion of antimony in the glass isrestricted to at most 0.19 cat.-%, further preferably to at most 0.18cat.-%, even further preferably to at most 0.17 cat.-%. The positiveeffects of a low antimony-content can also be inferred from the resultsof example 6. However, preferably at least 0.02 cat.-%, furtherpreferably at least 0.05 cat.-%, further preferably at least 0.08cat.-%, further preferably at least 0.09 cat.-%, further preferably atleast 0.1 cat.-% and particularly preferably at least 0.15 cat.-% areused for a particularly fine distribution of the nuclei-source in theglass. In an alternative embodiment, the glass is free of antimony.

Via an advantageous selection of the antimony-content a glass may beobtained, whose transmittance value at 260 nm and a sample thickness of1 mm is preferably at least 1.2%, further preferably at least 1.5%,further preferably at least 1.8%, further preferably at least 2%,further preferably at least 2.5%. Furthermore, when the antimony-contentis advantageously selected, the light exposure time, which is necessaryfor achieving sufficient crystallization at a light exposure dosepreferred according to the present invention is at most 15 minutes, atmost 10 minutes, further preferred at most 5 minutes. Via anadvantageous selection of the antimony-content according to the presentinvention a glass may preferably be obtained, at which upon lightexposure with UV-light a light exposure depth of at least 1 mm, furtherpreferred at most 2 mm, further preferred at most 2.5 mm, furtherpreferred at most 3 mm, further preferred at most 4 mm, even furtherpreferred 5 mm may be achieved.

As indicated at the beginning the glass of the invention comprises atleast one pair of nucleating agents in addition to silicon,crystal-agonists and crystal-antagonists. The pair of nucleating agentson the other hand comprises a nuclei-source, which is preferablyselected from silver, gold and copper as well as a reducing agent, whichis cerium according to the present invention. Silver is preferred asnuclei-source. The roles that these two components play in the pair ofnucleating agents can be inferred from Equation 1 exemplarily presentedabove for the pair of nucleating agents cerium and silver. In summary,it is about that the reducing agent reduces the cations of thenuclei-source to metal, whereby in the glass nuclei are formed, which inturn shall enable crystal formation.

It is preferred according to the invention that the amount ofnuclei-source in the glass of the invention is comparably high.Background is that many small finely distributed nuclei lead to a finercrystal arrangement than a smaller number of nuclei in the same glassvolume. For this reason the amount of nuclei-source in the glass, whichis preferably silver ions, should have a proportion of at least 0.001cat.-%. Further preferably this proportion is at least 0.01 cat.-%, morepreferably at least 0.03 cat.-%, particularly preferably at least 0.05cat.-%. However, if the amount of nuclei-source is chosen too high,nuclei formation or precipitation of elemental metal, respectively,possibly occurs already during melting. This has to be prevented by allmeans because precipitated metal droplets are firstly not available fornuclei formation in the glass and secondly the glass does not have theoptical quality that is necessary. Furthermore, elemental metal dropletsimpair the transmittance properties of the glass for example by lightscattering. Therefore, the amount of nuclei-source in the glass of theinvention is preferably restricted to at most 0.5 cat.-% or at most 0.2cat.-%, further preferred at most 0.1 cat.-% and particularly preferredat most 0.08 cat.-%. In preferred embodiments the glass is free of goldand/or copper.

As explained it is desirable to achieve a large number of nuclei in agiven volume after light exposure; however, the nuclei shall be formedonly in the light exposed areas. Because of the reaction equationpresented above it is not sufficient for this purpose to choose theproportion of nuclei-source as high as possible. Rather it is alsonecessary to perform the sensitization of the invention and to adjustthe proportion of Ce³⁺ to the amount of nuclei-source used. According tothe invention it is therefore preferred that the molar ratio ofnuclei-source to cerium (total amount Ce³⁺ and Ce⁴⁺) in the glass of theinvention is at most 10, further preferred at most 7, more preferred atmost 6.5 and particularly preferred at most 5.8. A larger amount ofnuclei-source may increase the problems at the production withoutconsiderably improving the fine crystallinity. However, the ratio shouldof course not be too low so that the amount of formed nuclei issufficient for enabling achievement of particularly fine structures inthe photo-structurable glass.

Because of the simplified process management during production of theglasses of the invention in comparison to the prior art the amount ofcerium in the glass can be chosen comparably high. Eventually ceriumwill be present to a certain degree in oxidation state 4+ due to therelatively oxidizing melting procedure. Thereby the undesired nucleiformation is suppressed during the manufacturing to a certain degree. Atthe same time, just as the amount of cerium, the amount of nuclei-sourcecan be chosen relatively high for achieving a fine crystal arrangement,which in turn enables a particularly fine structuring.

The amount of cerium (as sum of Ce³⁺ and Ce⁴⁺) in the glass of theinvention is accordingly preferably at least 0.001 cat.-%, furtherpreferably at least 0.005 cat.-%, more preferably at least 0.008 cat.-%and particularly preferably at least 0.01 cat.-%. The glasses of theinvention shall be photo-structurable. This means that they, afterexposure to UV-light of a certain wave-length and a subsequent temperingstep, can be selectively crystallized and subsequently structured(etched). However, the proportion of cerium in the glass of theinvention must not be increased at will because thereby indeed thephoto-sensitivity would be increased, however also the transmissibilityof the UV-light of relevant wave-length would be suppressed. Eventually,for light exposure of the glasses of the invention (as in the prior art)UV-light of a wave-length is used, at which Ce³⁺ is absorbing. Thus, ifthe content of Ce³⁺ in the glass of the invention is very high, itcannot be light exposed in any desired depth. This reduces the maximallyachievable structure depth. For this reason the content of cerium in theglass is preferably restricted to at most 0.3 cat.-% or at most 0.2cat.-%, further preferred at most 0.1 cat.-%, more preferred at most0.05 cat.-% and particularly preferred at most 0.025 cat.-%. In orderfor the desired effect according to Equation 1 to occur, cerium shouldbe present in the glass of the invention in an amount of at least 0.001cat.-%, in particular at least 0.005 cat.-% and particularly preferredeven at least 0.08 cat.-% or 0.01 cat.-%. In the prior art it was triedto achieve the crystallization susceptibility by reduction of the amountof nuclei former. This definitely works, however the photo-sensitivityof the glasses is thereby restricted so much that structuring isstrongly impeded.

Preferably, the molar content of nuclei-source in the glass is at leasttwice as high as the content of cerium, further preferably the molarratio of nuclei-source to cerium is at least 2.2, more preferably atleast 2.5 and particularly preferably at least 3 and in particular atleast 4.5. Advantages at crystallization arise from a balanced ratio ofnuclei-source, in particular silver, to cerium. At presence of arelatively larger amount of nuclei-source more nuclei are formed, whichin turn leads to smaller crystals. The content of cerium relative tonuclei-source is rather small according to the invention because noparticularly large amount of this component is necessary for nucleiformation due to the sensitization. However, the indicated ratio ofsilver to cerium should not exceed a certain value because otherwise therelative amount of cerium is not sufficient for inducing sufficientformation of nuclei.

In special embodiments it may be reasonable to further restrict theratio of nuclei-source to cerium. This is the case in particular whenonly a smaller structure depth can be achieved by UV light exposure. Anincrease in the achievable structure depth can on the one hand indeed beachieved by reduction of the cerium-content as described above. However,it was surprisingly found that also without reduction of thecerium-content an increased structure depth can be achieved if a lowerratio of nuclei-source to cerium is chosen. This can be reasonable incomparison to a reduction of the cerium-content because thereby there isstill enough Ce³⁺ available as reducing agent for Ag⁺ even at arelatively oxidizing melting procedure and consequently a relativelyhigh Ce⁴⁺/Ce³⁺ ratio due to the relatively high total content of cerium.In such an embodiment the ratio of nuclei-source to cerium in the glassof the present invention is preferably at most 5.5, further preferablyat most 5.2, particularly preferably at most 4.9.

The list of glass components as indicated herein is not conclusive.Thus, the glass of the invention may contain further components notmentioned herein. However, in preferred embodiments with regard to thecations the glass of the invention consists to an extent of at least 90cat.-% of the components mentioned herein. In further preferredembodiments, the glass of the invention consists to at least 95 cat.-%,further preferred at least 97 cat.-%, more preferred at least 99 cat.-%of the components mentioned herein. In a particularly preferredembodiment the glass of the invention consists to 100 cat.-% of thecomponents discussed herein.

Preferably, the glass is free of molecular hydrogen (H₂). Molecularhydrogen can lead to formation of atomic silver and thus to nucleiformation independent of irradiation.

If it is indicated in this description that the glass does not contain acertain component or is free of a certain component, then it is meantthat this component is not added to the glass intentionally. This doesnot exclude that this component is possibly present in the glass asimpurity. Impurities shall typically and preferably not exceed aproportion of 0.1% by weight of the glass, further preferred not morethan 100 ppm, more preferably not more than 10 ppm, even more preferrednot more than 1 ppm shall be present. In a preferred embodiment, thethus indicated components are present in the glass of the invention atmost in an amount that is below the detection limit.

A preferable glass of the invention comprises the following componentsin cat.-%:

Si⁴⁺ 45 to 65 Crystal-agonists 30 to 45 Crystal-antagonists 3.5 to 9 

In a preferred embodiment the glass of the invention comprises thefollowing components in cat.-%:

Si⁴⁺ 45 to 65 Crystal-agonists Li⁺ 25 to 40 K⁺ 0 to 8 Na⁺ 0 to 8Crystal-antagonists B³⁺ 0 to 5 Al³⁺  0 to 10 Zn²⁺ 0 to 4 Sb³⁺  0 to 0.4Nuclei-source Ce³⁺/Ce⁴⁺  >0 to 0.3 Ag⁺  >0 to 0.5

In addition to cations the glass of the invention also comprises anions,which are preferably selected from the group consisting of O²⁻, F⁻, Br⁻,Cl⁻ and SO₄ ²⁻. The molar proportion of O²⁻ with regard to the anionsshould preferably be at least 50% (anion-%), further preferably at least70%, more preferably at least 90%, more preferably at least 98% andparticularly preferably at least 99%. In a preferred embodiment theglass is entirely oxidic, it thus contains only O²⁻ as anions and isfree of other anions.

The glass of the invention preferably comprises only small amounts ofhalides. It is preferred that the content of halides among the anions isrestricted to at most 5 anion-%, further preferably at most 3 anion-%and more preferably at most 1 anion-%. Halides are understood accordingto the invention as the anions of CI, F and Br. In particularembodiments the glass is free of anions of CI, F and/or Br or comprisesthese components in proportions of preferably not more than 3 anion-%, 2anion-% or 1 anion-% each.

The glass of this invention preferably comprises essentially nocolloidal silver prior to irradiation with UV-light. The silverpreferably present in the glass is in particular present prior toirradiation in form of Ag⁺ in a proportion of at least 95%, furtherpreferred at least 99%.

The glass of this invention should preferably not contain more than 5cat.-% T⁴⁺ (titanium). Titanium impairs transmittance of the glasses inthe UV region, which negatively affects the achievable structure depth.Preferably, the content of titanium is restricted to at most 3 cat.-%,further preferred at most 1 cat.-%. Preferred embodiments comprisetitanium in amounts of less than 0.2 cat.-% or are free of titanium.

The glass of the invention is preferably free of components notmentioned herein, in particular of cations of Fe, Ni, Co, La, Nb, W, Hf,Bi, Y, Yb, Pb, As, Ta, Gd and/or Eu.

It turned out to be advantageous to restrict the content of alkalineearth metal cations in the glass of the invention, in particular to upto 10 cat.-%, preferably up to 5 cat.-%, more preferably up to 2 cat.-%.In particularly preferred embodiments the glass comprises at most 1cat.-% of alkaline earth metal cations or is even free of these.Alkaline earth metal cations are preferably understood according to theinvention as Mg²⁺, Ca²⁺, Ba²⁺ and Sr²⁺. In special embodiments the glassis free of Mg²⁺, Ca²⁺, Ba²⁺ and/or Sr²⁺ or comprises these components inproportions of preferably not more than 3 cat.-%, 2 cat.-% or 1 cat.-%each. In preferred embodiments the glass is free of barium.

The glasses of the present invention are either cooled relatively slowlyduring cooling of the melt or after fast cooling of the melt they areonce more heated to the temperature T1 and are slowly cooled from thereto the temperature T2 in a post-processing step. In the context of thisinvention we call these alternative process steps “sensitization”.

Sensitization is characterized by the glass being cooled from theinitial temperature T1 to the target temperature T2. Thereby the initialtemperature T1 is in a range that allows diffusion of ions in the glassto a certain extent, this is a temperature range, which is at leastabove the glass transition temperature T_(g) of the glass, in particularat least 25° C. above T_(g). By controlled, slow cooling from T1 to T2,the cooling state of the glass is adjusted. Only at reaching the targettemperature T2, which is at least 150° C. below T1, the viscosity in theglass is preferably again so high that no further diffusion and nofurther change of the cooling state of the glass occurs anymore.

In preferred embodiments the initial temperature T1 is at least 400° C.,further preferably at least 425° C., more preferably at least 450° C.and particularly preferably at least 475° C. A certain minimumtemperature is necessary for enabling the adjustment of the coolingstate. Therefore, T1 has to be above T_(g) of the glass. In preferredembodiments T1 is at least 25° C., further preferred at least 40° C.above T_(g). However, at too high temperatures the crystallizationtendency increases so that a too high temperature T1 may lead tocrystallization. Therefore, T1 preferably does not exceed a value of1000° C., further preferably 800° C., more preferably 600° C. andparticularly preferably 550° C. In particularly preferred embodiments isT1=500° C. T1 is preferably below the softening temperature of theglass, in particular at least 100° C. below the softening temperature.

Temperature T2 is at least 150° C. below T1. T2 is preferably belowT_(g) of the glass. In preferred embodiments T2 is at least 20° C.,further preferred at least 100° C., more preferred at least 200° C. andparticularly preferred at least 220° C. In order that the ion mobilityat T2 decreases again to a negligibly small value it is preferred thatT2 is at most 400° C., further preferred at most 350° C., more preferredat most 300° C. In a particularly preferred embodiment is T2=240° C.

The sensitization performed in accordance with the invention leads tothe cooling state of the invention. For that the sensitization comprisescooling of the glass either from the melt or as post-processing on aglass body. Accordingly the glass is for example cooled from the melt toT1 or a glass body is heated to T1, and afterwards it is cooled to T2.Subsequently, the glass is cooled from T2 to room temperature ifapplicable.

In an embodiment the glass is cooled during sensitization steadily fromtemperature T1 to T2. “Steadily” means therein that it is cooledcontinuously from T1 to T2 without maintaining the glass at certaintemperature levels. In particular therewith is meant a cooling withessentially constant cooling rate. As far as it is further cooled fromT2 to room temperature also this further cooling can occur steadily.Room temperature is preferably 20° C.

In another embodiment the glass passes through different cooling stagesduring sensitization. Thereby the glass is preferably cooled fromtemperature T1 to a temperature T1.1, then to a temperature T1.2 and soon. Thereby it is preferred that the glass is cooled via at least 2intermediate stages, in particular at least 3 and particularly preferredat least 4 intermediate stages to temperature T2. However, preferably itis cooled via at most 7, further preferred at most 6 and particularlypreferred at most 5 intermediate stages. In such an embodiment the glassmay be cooled by passing through at least one cooling furnace. Thisenables a continuous processing. Preferably sensitization occurs in sucha way that the glass is lead through zones of different temperatures forensuring the cooling. Therein this way of cooling means optionally butnot necessarily that also the temperature of the glass is kept at thetemperature of the respective stage. Rather, the temperature of theglass within a temperature stage may slowly adapt to the temperature ofthis stage and then be moved into the next stage. This may beimplemented as a cooling sequence by use of temperature zones on acooling line.

When passing through different cooling stages, the glass is preferablykept for 10 to 40 minutes at a given temperature stage. The temperaturestages preferably have a distance of at least 5° C. and in particular atleast 10° C. and in particular at most 50° C. Thereby the glass does notnecessarily reach the temperature of the respective stage before it istransferred to the next temperature stage.

The sensitization of the glass of the invention may thus occur eitherdirectly from the melt, the initial temperature T1 is thus then reachedby cooling of the glass from the melt, or the sensitization takes placeas separate post-processing step, as the glass is re-heated to theinitial temperature T1 and then controlledly cooled to T2.

Sensitization as a post-processing step has the advantage that the glassmay be subjected prior to sensitization to other processing steps, asfor example hot forming processes, which would be hardly possibleotherwise due to the crystallization tendency. Prior to sensitizationthe crystallization tendency of the glass of the invention is not sopronounced as after the sensitization.

For example, the glass of the invention may initially be melted and thenquickly cooled from the melt. Such cooled glass may then be drawn in aredrawing method without crystallizing. The redrawn glass element maythen be sensitized prior to light exposure.

When sensitization is discussed herein, this always means a processingstep that occurs prior to the light exposure of the glass. The heattreatment step after light exposure is herein called “tempering” inagreement with the literature.

The cooling state of the glass of the invention is adjusted by thesensitization. Thereby also the density of the glass approaches thedensity of the underlying crystal system. The glass is getting denser.This relates to both the mass density and the index of refraction. Theglasses of the invention preferably have a refractive index η_(d) at546.1 nm and 25° C. of at least 1.500 and preferably at most 1.600.Furthermore, the glasses preferably have a mass density p of at least2.35 g/cm³, further preferred at least 2.36 g/cm³. In preferredembodiments the density is less than 2.4 g/cm³ and preferably less than2.39 g/cm³. High density results in formation of smaller crystallitesafter light exposure and tempering due to suppressed diffusion of thecrystal components, however, the closer the density approaches thedensity of the crystals, the higher is also the risk of undesired,non-selective crystallization. If not indicated otherwise orautomatically evident for the skilled person, measurements herein areperformed at a temperature of 25° C. and an air pressure of 101.325 kPa.

The glasses of the invention preferably have a softening point of atleast 600° C., in particular at least 650° C. Preferably, the softeningpoint is at most 750° C. and in particular at most 700° C.

As described above, the glass of the invention is melted in a comparablyoxidizing way. Thereby the component cerium is also present in itstetravalent oxidation state. However, the tetravalent oxidation statedoes not participate in the above described reaction (Equation 1) ofnuclei formation. Apparently, the proportion of cerium in the trivalentoxidation state increases in the glass of the invention by thesensitization. Ce³⁺ absorbs at about 314 nm, thus in the UV. In orderfor the glass to form a high number of nuclei upon light exposure, it ispreferred according to the invention, that the glass of the inventionhas a transmittance of not more than 50% at a wavelength of 314 nm and athickness of 1 mm.

Particularly preferably, the transmittance at 314 nm and a thickness of1 mm is not more than 40%, further preferred not more than 39%.Nevertheless, the absorption at this wavelength should not be too highso that the UV radiation may enter the glass deep enough for achievingdeep structures. In this respect the transmittance at 314 nm and athickness of 1 mm should preferably be at least 10%, further preferredat least 20%, more preferred at least 25% or at least 30% andparticularly preferred at least 35%. The transmittance is in particularthe internal transmittance, thus the transmittance of the glass withoutinfluences of reflections. The transmittance of an example glass isshown in FIG. 4 in dependence from the wave-length.

In order for this to be achieved, it is preferred according to theinvention, that the amount of cerium in the glass of the invention isrestricted. The content of cerium should be selected depending on thethickness of the glass. In preferred embodiments, the content of ceriumin the glass of the invention is restricted to an amount of at most4×10⁻³ cat.-% per millimeter glass thickness. Further preferred is avalue of at most 3×10⁻³ cat.-% per millimeter glass thickness. However,in order for the amount of cerium being sufficient for triggering theparticularly advantageous formation of nuclei, a minimum amount ofcerium of at least 2×10⁻³ cat.-% per millimeter glass thickness shouldbe set up. Preferably, the glass of the invention is present with athickness of at least 1 mm, further preferred at least 3 mm andparticularly preferred at least 5 mm. However, the thickness preferablydoes not exceed a value of 20 mm, further preferably 15 mm.

The method of the invention for producing the glasses of the inventioncomprises the following steps: Mixing the respective raw materials forobtaining a mixture, Melting the mixture for obtaining a melt,Solidifying the melt for obtaining a glass.

It is an advantage of the glasses of the invention that they areproducible in a continuous production method. Preferably, melting of themixture occurs in a vessel. From there the glass melt preferably reachesa refining vessel, where a refining step takes place. From the refiningvessel the glass melt preferably reaches a crucible, in particular aplatinum crucible, which may have a stirrer. The glass melt ishomogenized in the crucible. By stirring a particularly high homogeneitycan be achieved.

In a preferred embodiment, the glass melt may get from the crucible intoa drawing vessel. Subsequently, for example a down draw, new down drawor overflow fusion process may be conducted. In any case, the product isa thin glass with fire-polished surfaces.

Fire-polished surfaces are normally characterized by an extremely lowroughness. Therefore, the surface of the glasses of the presentinvention preferably has a roughness Ra of less than 5 nm, furtherpreferred less than 2 nm, further preferred less than 1.5 nm, furtherpreferred less than 1 nm, further preferred less than 0.8 nm, furtherpreferred less than 0.5 nm, further preferred less than 0.2 nm, morepreferred less than 0.1 nm. Preferably, roughness is measured with anoptical profilometer.

In case of down draw, the glass exits via a slit in the bottom of thedrawing vessel, which is equipped with sword-shaped leading elements incase of new down draw. In case of overflow fusion, the glass exits viathe upper rims of the drawing vessel and runs down the outer walls ofthe vessel. These methods are known to the skilled person.

In accordance with the invention is thus in particular a method forproducing a glass of the invention comprising the steps: Producing aglass melt, Transferring the melt into a drawing vessel, Allowing themelt to exit the drawing vessel, Drawing the exiting melt to a glasssheet, and Cooling the glass sheet, wherein the melt at the time ofexiting the drawing vessel preferably has a temperature that is above1000° C.

Alternatively, the melt can be removed from the crucible forsolidification. In an embodiment, the glass is formed subsequent meltingbut prior to solidification. In such an alternative embodiment the glassmelt preferably gets into a mold via an outlet. In the mold the glasssolidifies into a blank (for example a glass bar). Alternatively, aglass body may be produced from the glass of the invention by pressingor rolling. A thus produced glass body may then be cut with a cuttingprocess, in particular by sawing, into glass wafers that subsequentlymay be ground and/or polished. A particularly preferred cutting processis wire-sawing, in particular multi-wire-sawing, for exampleMulti-Wire-Slice (MWS). Preferred cutting material is steel wire. Inpreferred embodiments the internal medium between raw glass and steelwire is emery. In such embodiments, the particle size of the internalmedium is preferably in the range between 100 and 300 US standard mesh,more preferred in the range between 150 and 250 US standard mesh, morepreferred about 200 US standard mesh. Preferably, the cutting speed isin the range between 2 and 20 mm/hour, more preferred between 4 and 15mm/hour, even more preferred between 6 and 10 mm/hour. If the cuttingspeed is very low, cutting is not very efficient. If the cutting speedis very high, the glass may break or the cutting wire may be torn apart.

Preferably, the cut glass wafers, optionally after grinding andpolishing, have total thickness variations (TTV) of at most 30 μm,further preferred at most 20 μm, further preferred at most 15 μm,further preferred at most 10 μm, further preferred at most 8 μm, furtherpreferred at most 5 μm in an area of 325 cm². Of course, the indicatedTTV is preferably all the more reached in smaller areas, as for examplein an area of 180 cm².

The above described sensitization of the glass may either take placeduring a forming process (pressing, down draw, overflow fusion), ascooling of the formed glass takes place according to the process step ofsensitization as described above, or initially quickly cooled glassbodies are produced, which are subsequently subjected to a process stepof sensitization. For example the glass melt may initially be cast intomolds and quickly cooled there. Subsequently, the thus obtained blanksmay be subjected to further hot forming via a redrawing method.Sensitization may then take place in this redrawing method. The glassbody is preferably not a laminate. The glass body preferably completelyconsists of the glass described herein and in particular does notconsist of ceramic or glass ceramic.

With the continuous production method glasses with particular highhomogeneity can be obtained because the occurrence of striae can bereduced drastically. Particularly small fluctuations with regard to thetransmittance, the density and the index of refraction result from suchhigh homogeneity. Preferably, the glass is so homogeneous that at awavelength of 260 nm and/or 280 nm the standard deviation of thetransmittance is at most 15%, further preferred at most 10%, furtherpreferred at most 7%, further preferred at most 5%, further preferred atmost 4%, further preferred at most 3%, even further preferred at most2%, particularly preferred at most 1%, even further preferred at most0.8%, even further preferred at most 0.5%, even further preferred atmost 0.4%, even further preferred at most 0.2% of the respective meanvalue of transmittance, wherein mean value and standard deviation aredetermined from at most 100, preferably at most 60, further preferred atmost 40, further preferred at most 30 independent measured values.Preferably, mean value and standard deviation are determined from atleast 5 independent measured values, more preferably from at least 10independent measured values, more preferably from at least 15independent measured values. In preferred embodiments, mean value andstandard deviation are determined from 50 independent measured values,more preferably from 40 independent measured values. The independentmeasured values are obtained by measuring transmittance on differentpositions of the glass. Preferably, the distance between any twoneighboring measuring positions is at least 0.1 mm, more preferably atleast 0.5 mm, more preferably at least 1 mm, more preferably at least 5mm, even more preferably at least 10 mm. The skilled person knows how todetermine the standard deviation based on a group of measured values.The standard deviation corresponds to the square root of the sum of thesquared deviations of the individual measured values from the mean valueof the measured values, wherein the sum is divided by the number ofmeasured values minus one prior to square rooting.

The transmittance value at 260 nm and a sample thickness of 1 mm ispreferably at least 0.2%, further preferred at least 0.5%, furtherpreferred at least 1%, further preferred at least 1.2%, furtherpreferred at least 1.5%, further preferred at least 1.8%, furtherpreferred at least 2%, further preferred at least 2.5%. Preferably, thetransmittance value at 260 nm and a sample thickness of 1 mm is at most5%, further preferred at most 4%, further preferred at most 3.5%,further preferred at most 3%. The transmittance value a 280 nm and asample thickness of 1 mm is preferably at least 8%, further preferred atleast 9%, further preferred at least 10%, further preferred at least11%, further preferred at least 12%, further preferred at least 13%,further preferred at least 15%, further preferred at least 16%.Preferably, the transmittance value at 280 nm and a sample thickness of1 mm is at most 30%, further preferred at most 25%, further preferred atmost 20%.

It is remarkable that even at wavelengths of 260 nm and 280 nmpreferably such low fluctuations of transmittance can be achievedbecause this is exactly where the UV-edge is and thus generally higherstandard deviations would be expected. Moreover, these wave-lengths areat least slightly overlapping with the absorption region of Ce³⁺ so thatthe small fluctuations of transmittance are a good indicator for thehomogeneous distribution within the glass.

Measurement of transmittance can preferably be used for quality testingof the glasses because only small deviations occur in the transmittancevalues. Furthermore, due to the possibility of improved optical focusingthe small fluctuations of the index of refraction preferably enable alight exposure of the glass body not only at its surface or insurface-near regions but also deep inside the glass body via arespectively focused laser. The high homogeneity of the glassespreferably also causes that more homogeneous etching rates are presentduring the etching process, which in turn may result in more preciselyobtainable structures due to a reduction of etching errors. Moreover, bya more homogeneous etching rate preferably also the occurrence ofetching-caused striae is reduced. The very low-striae manufacturingfacilitates the applicability of the indicated methods.

Due to the production in a continuous process not only the abovedescribed homogeneity within a glass piece is increased but also thehomogeneity between different batches.

For adjusting the redox state of the glass melt the used raw materialsare important. The following list indicates the respectively preferablyused raw materials for adjusting suitable melting conditions. However,the skilled person is also familiar with other measures for adjustingthe redox conditions of the melt. For example, in an embodiment of theinvention oxidizing gases may be conducted into the melt (bubbling).Furthermore, the temperature of the melt is important for the redoxstate. In particular, high melting temperatures result in reducingmelting conditions.

Glass component Preferred raw material Si⁴⁺ Sand Crystal-agonists Li⁺Lithium carbonate K⁺ Potash Na⁺ Soda, sodium sulfate, sodium antimonateCrystal-antagonists B³⁺ Boron trioxide Al³⁺ Aluminum hydroxide Zn²⁺ Zincoxide Sb³⁺ Sodium hexahydroxidoantimonate Nuclei-former Ce³⁺/Ce⁴⁺ Ceriumoxide Ag⁺ Silver oxide, silver nitrate

Depending on the desired composition of anions in the glass of theinvention, also the respective halides may be used. It is howeverpreferred according to the invention that the glasses comprise as littleproportions of halides as possible.

The invention also comprises a method for photo-structuring a glass ofthe invention. The method of photo-structuring comprises in particularthe steps of light exposure, tempering and structuring of a glass body,which comprises the glass of the invention and in particular consiststhereof. The light exposure preferably occurs at a wavelength, whichessentially corresponds to the absorption maximum of Ce³⁺ in the glassof the invention. This wavelength is in the UV, in particular in theregion between 300 nm and 320 nm, in particular at 310 nm. During lightexposure, regions that are not to be light exposed are preferablycovered with a mask.

The dose of UV light exposure has to be high enough for ensuring asufficient photo-structuring. The UV light exposure preferably takesplace with a dose of more than 0.1 J/cm². Further preferred the dose isat least 1 J/cm², further preferred at least 3 J/cm², further preferredat least 5 J/cm², further preferred at least 7 J/cm², even furtherpreferred at least 10 J/cm². However, the dose should also not be toohigh. Preferably, the dose is at most 100 J/cm², further preferred atmost 50 J/cm², even further preferred at most 25 J/cm².

Preferably the light exposure time, which is necessary for a sufficientcrystallization at a dose preferred according to the invention, is atmost 20 minutes, further preferred at most 15 minutes, further preferredat most 10 minutes, further preferred at most 5 minutes.

In a preferred embodiment the light exposure takes place with a laser.Preferably, the laser is a pulsed laser. Preferably, the laser is ananosecond-laser, further preferred a picosecond-laser, even furtherpreferred a femtosecond-laser. Multi-photon absorption enables workingwith long wavelength in the visible range or more preferred even inIR-range, at which ranges the glass has a particular high transmittanceso that it can be light exposed in great depths. The excitation ofcomponents in the UV-region, as for example Ce³⁺, occurs in suchembodiments preferably very predominantly in the regions onto which thelaser is focused. Very particularly preferably, the laser is atitanium:sapphire-femtosecond-laser. Light exposure with a laserpreferably additionally enables generation of particularly finestructures and/or structures being particularly deep inside the glassbody in the subsequent etching step.

The high homogeneity of the glasses produced according to the method ofthe present invention, in particular with regard to the transmittanceand to the index of refraction, preferably enables a light exposure alsoin great depths within the glass body. The light exposure preferablyoccurs with a focused short-pulse laser or with a UV-source, for examplea UV-lamp or a UV-burner. Preferably, the light exposure depth is atleast 0.5 mm, further preferred at least 1 mm, further preferred atleast 2 mm, further preferred at least 5 mm, further preferred at least10 mm, further preferred at least 15 mm, further preferred at least 20mm. Preferably, the light exposure depth is even up to 50 mm, furtherpreferred up to 100 mm, further preferred up to 200 mm, furtherpreferred up to 300 mm, further preferred up to 500 mm, furtherpreferred up to 1000 mm, even further preferred up to 2500 mm. However,it has to be considered that the focus of the short-pulse laser isgetting longer or blurred with increasing light exposure depth.Therefore, light exposure with a focused short-pulse laser should alsonot occur in too great depth. The light exposure depth is preferablydetermined via the depth of the light exposure dependentcrystallization. The measurement is conducted for the side view. Theglass body is exposed on its entire surface with the UV illumination.Then the glass body is tempered in order to crystallize the exposedparts. Then the sample is cut in half, and the cleaved part is inspectedfrom the side. Preferably, immersion oil is used in order to avoid thenecessity of polishing the cleaved surface. The exposure depth is thenmeasured with a microscope. The border of crystallization can clearly beseen by this method.

Particularly preferably undercut structures may be generated. For this,preferably different UV-lasers are used, which differ with regard to theentering depth into the glass body. Hence, it can be light exposed indifferent depths with different doses. Because the actual structuringoccurs in a subsequent etching step, preferably already two, furtherpreferably even a single round of light exposure is sufficient so thathigh velocities of light exposure of preferably at least 1 m/s, morepreferably at least 5 m/s, even more preferably at least 10 m/s can beachieved. Preferably, a wafer can be processed in less than 12 hours,more preferred less than 6 hours, more preferred less than 3 hours, morepreferred less than 2 hours, more preferred less than 1 hour. Bystepwise ceramization of an already structured element, preferably alsopredetermined breaking points can be generated.

The structuring of the light exposed glass body preferably occurs viaetching, in particular with an HF-containing etching solution. Theconcentration of HF in the etching solution is preferably between 5% and20% by weight in water. Particularly preferably the concentration of HFin the etching solution is 10% by weight. By the structuring structuredglass bodies are obtained, which in comparison to the prior art have abetter, at least however an equivalent structure with respect to thestructure depth and to the aspect ratio.

The structure depth in the structured glass bodies, which are availablewith the glass according to the invention, is preferably up to 0.1 mm,further preferred up to 0.2 mm, more preferred up to 0.5 mm, morepreferred up to 1 mm, more preferred up to 2 mm, more preferred up to 3mm, even more preferred up to 4 mm, very particularly preferred up to 5mm. “Structure depth” is understood according to the invention as theheight difference in the direction of etching between a crystallizedregion and a non-crystallized region.

“Aspect ratio” is understood according to the present invention as theration between the depth of a structure and its width. Of course it ispreferable when large aspect ratios are possible. With the glass of thepresent invention aspect ratios of up to 80 to 1, preferably up to 60 to1, more preferably up to 50 to 1 and particularly preferably up to 40 to1 can be achieved. Preferably the achievable aspect ratio is at least 10to 1, further preferred at least 15 to 1, further preferred at least 20to 1.

The transmittance of the glass at the wavelength of light exposureshould be as high as possible so that particularly large structuredepths can be achieved. Therefore, the above indicated parameters withregard to transmittance should be observed when large structure depth isdesired. For the transmittance at the wavelength of light exposure theamount of Ce³⁺ is important among others.

After light exposure and prior to structuring the glass bodies to bestructured are preferably tempered. Tempering serves for inducingcrystal formation around the nuclei formed during light exposure. Forthis purpose the glass body to be structured is heated to a temperature,which enables formation of crystals and which is in particular above theglass transition temperature of the glass. This temperature ispreferably at least 400° C., further preferred at least 455° C., furtherpreferred at least 500° C., further preferred at least 550° C.Furthermore, this temperature should preferably not exceed a value of650° C., further preferred 600° C. and particularly preferred 580° C.Very particularly preferred this temperature is in a range of from 555°C. to 565° C., even more preferred the temperature is 560° C. Eventhough the etching ratio may be higher at high temperatures, theindicated preferred tempering temperatures are nonetheless preferredbecause crystallization may occur to a larger extend also in areas thatwere not light exposed in case the tempering temperature is very high.Furthermore, a certain holding time in this temperature range should beobserved so that sufficient crystals of the desired size may form. Theholding time is preferably at least 10 minutes. Generally not enoughcrystals form at a too low temperature or a too short holding time andthe crystal growth is too strongly pronounced at too high temperature ortoo long holding time so that particular large crystals are obtained.Large crystals are disadvantageous because they lead to the structuredsurface having a comparably high roughness. Thus, small crystals arepreferred. Particularly preferably, after the etching process thesurface has a roughness Ra of less than 1000 nm, further preferred lessthan 100 nm, further preferred less than 50 nm, further preferred lessthan 20 nm, further preferred less than 10 nm, further preferred lessthan 5 nm, further preferred less than 3 nm, further preferred less than1 nm. Preferably, the roughness is measured with a tactile profilometer.Particularly preferably, the roughness is measured with a Dektak XT™stylus profiler by BRUKER.

The etching rate describes the removal from the surface of the glassbody by the etching solution. The unit of the etching rate is μm/min.Structuring of the surface is achieved by the etching rate being higherin the regions that have before been light exposed with UV radiationthan in the unexposed regions. Preferably, the etching rate in theunexposed regions is at most 5 μm/min, more preferably at most 2 μm/min,more preferably at most 1 μm/min, even more preferably at most 0.5μm/min. In the light exposed regions the etching rate is preferably atleast 10 μm/min, more preferably at least 20 μm/min, more preferably atleast 30 μm/min, more preferably at least 40 μm/min, even morepreferably at least 50 μm/min.

The etching ratio is the ratio of the etching rate in the light exposedregions to the etching rate in the unexposed regions. Preferably, theetching ratio is at least 10 to 1, more preferably at least 20 to 1,more preferably at least 30 to 1, more preferably at least 40 to 1, evenmore preferably at least 50 to 1.

Due to the sensitization of the glass according to the present inventionin particular very pronounced crystal phases are formed. Indeed in thelight exposed regions it is not a pure ceramic but a mixture of glassand crystals (glass-ceramic). However, the proportion of crystals inthis glass-ceramic phase is particularly high according to theinvention. In the crystallized glass body of the present invention theproportion of crystals in the glass-ceramic phase is preferably at least10 vol.-%, further preferred at least 20 vol.-%, more preferred at least40 vol.-% and particularly preferred at least 60 vol.-%. However, theproportion of crystals in the glass-ceramic phase is smaller than 100vol.-%.

In one embodiment of the method of the invention for structuring ofglass bodies, glass bodies are used, which have been formed before in ahot forming method. Examples for such hot forming methods, which arepreferably used according to the present invention, are pressing, downdraw, new down draw, overflow fusion and redrawing. Particularlypreferred are down draw, new down draw and overflow fusion. Thesemethods are known to the skilled person. However, they could not beperformed with photo-structurable glasses of the prior art because allof these methods have to be performed at temperatures, which favor acrystallization of the glass. However, the glasses of the invention canbe subjected to a hot forming process in an “insensitive” state and canbe sensitized only subsequently. During hot forming the crystallizationtendency of the glasses of the invention is not so pronounced thatcrystallization occurs. Only upon sensitization, which is describedfurther above, the crystallization tendency is increased in such a waythat photo-structuring becomes possible.

Consequently, a method preferred according to the invention comprises:initially melting the glass, subsequently hot forming, sensitization ofthe glass during hot forming or subsequently and subsequently thestructuring as described above.

A structured glass body, which has excellent properties with regard todurability, structure depth, aspect ratio and internal quality, is thenobtained from the glass of the invention.

Particularly preferred structures are through holes. Through holes areholes that extend through the entire thickness of a glass body.Preferably, through holes have an essentially cylindrical shape, whereinthe height of the cylinder corresponds to the thickness of the glassbody. The diameter of a through hole is the largest distance of opposingrims of the hole when measured perpendicular to the height axis of thehole. The shape of the through holes may deviate from the cylindricalshape. For example, the through holes may have essentially cuboid shape.However, in any case the diameter of the through hole is defined as thelargest distance of opposing rims of the hole when measuredperpendicular to the height axis of the hole. Preferably, the throughhole diameter is determined microscopically. In a preferred embodimentthrough holes with a diameter of at most 500 μm, further preferred atmost 250 μm, further preferred at most 100 μm, further preferred of atmost 50 μm, further preferred at most 35 μm, further preferred at most30 μm, even further preferred at most 20 μm, even further preferred atmost 10 μm can be obtained. Preferably, holes can be obtained, which areso close to each other that the distance of their centers has a value ofat most 1.5-times the hole-diameter. Further preferably the distance iseven only at most 1.3-times, further preferred at most 1.2-times, evenfurther preferred at most 1.1-times the hole-diameter. Preferably, holescan be generated with such a precision that at a designed hole-diameterof 30 μm and a glass thickness of 500 μm the deviations from thedesigned hole-diameter are at most 30 μm, more preferably at most 15 μm,more preferably at most 10 μm, more preferably at most 5 μm, morepreferably at most 2 μm, more preferably at most 1 μm, even morepreferably at most 0.5 μm. Due to such a precision also the deviationsof the diameter of individual through holes in a glass body of theinvention at a designed hole-diameter of 30 μm and a glass thickness of500 μm is preferably at most 30 μm, more preferably at most 15 μm, morepreferably at most 10 μm, more preferably at most 5 μm, more preferablyat most 2 μm, more preferably at most 1 μm, even more preferably at most0.5 μm. Preferably, through holes with so low deviations from thedesigned hole-diameter may be obtained that the standard deviation fromthe designed hole-diameter is at most 5 μm, further preferably at most 3μm, further preferably at most 2 μm, further preferably at most 1 μm,further preferably at most 0.5 μm, further preferably at most 0.2 μm,even further preferably at most 0.1 μm. Furthermore, at a designedhole-diameter of 30 μm and a glass thickness of 500 μm preferablythrough holes can be obtained, whose slope angle is smaller than 5°,more preferably smaller than 2°, even more preferably smaller than 1°,particularly preferably smaller than 0.5°. The slope angle describes thedeviation of the longitudinal direction of the through holes from theperpendicular to the surface of the glass bodies.

In accordance with the invention is also a glass body that may bephoto-structured and that is particularly thin because the glasses ofthe present invention are producible via hot forming methods, whichenable production of particularly flat glass bodies. Such a glass bodypreferably has a thickness that is at most 10 mm, further preferred atmost 5 mm, further preferred at most 2 mm, further preferred at most 1mm, further preferred at most 500 μm, further preferred at most 300 μm.Such glass bodies have been available so far only by cutting andpolishing. However, the surface qualities of the invention with regardto roughness of the glass body are not achievable by cutting andpolishing. Moreover, cutting and polishing is an energy-intensiveprocess that is accompanied by high costs.

The glasses of the invention can be applied in the field ofmicro-fluidics. For example, samples can be analyzed inside thephoto-structured glass bodies. For this purpose it is advantageous whenthe glasses have a good transmissibility to infrared radiation. Usinginfrared radiation, different qualitative and quantitative microscopicdetections can be performed. It is preferred according to the inventionthat the glasses of this invention have at a wavelength of 900 nm and athickness of 1 cm a transmission of at least 70%.

Furthermore, the glasses are preferably also transparent in the regionof visible light from 400 to 800 nm. This means preferably that theinternal transmittance of the glass in the entire wavelength region from400 nm to 800 nm at a thickness of 1 cm is always at least 85%, morepreferred at least 90% and particularly preferred at least 95%.

The glasses of the present invention may be used structured and/orunstructured in different applications. Preferred in accordance with theinvention is the use in components or as components in micro-technology,in micro-reaction-technology, in electronic packaging, for micro-fluidiccomponents, in or as FED spacer, for bio-technology (for example titerplates), as interposer, in or as three-dimensional structurableantennae.

Preferably, glass bodies of the present invention may be used assubstrates or glass circuit boards (GCB) in the fields ofmicrofluidics/biotechnology, for example: Lab-on-chip/Organ-on-chip,Micro Mixers, Micro Reactor, Printer head, Titer plates, Chipelectrophoresis, semiconductors, for example Logic/Integrated Circuits,Memory, Contact Image Sensor, Field emission display (FED) spacer,Integrated Passive Device (IPD), Capacitors, Inductors, Resistors,sensors, for example Flow-/temperature-sensors,Gyroscopes/Accelerometers, radio frequency micro-electromechanicalsystems (RF/MEMS), for example Antenna, Capacitor Filter/duplexer,Switches, Oscillator, Telecommunication for example Optic alignmentchips. Optical waveguides, Optical interconnects.

In accordance with the invention is also the use of the glass of theinvention in a method for production of a structured glass body.

EXAMPLES

The following table shows the compositions in cat.-% of glasses of theinvention. All of the presented glasses are oxidic, which means theproportion of anions that are not oxygen is at most 2 anion-%.

TABLE 1 EXAMPLE GLASSES IN CAT.-% Component B1 B2 B3 B4 B5 Si⁴⁺ 59.652.1 60.4 53 60.1 K⁺ 3.8 5.6 3.4 3.78 4.08 Na⁺ 2.5 2.8 0.15 3.79 2.51Ag⁺ 0.06 0.06 0.004 0.044 0.043 B³⁺ 0.26 0.94 0 0 0 Al³⁺ 3.8 5.14 4.276.05 3.86 Li⁺ 29.2 32.2 31.4 33.3 28.8 Σ(Ce⁴⁺, Ce³⁺) 0.011 0.01 0.0030.007 0.005 Zn²⁺ 0.56 1.07 0.27 0 0.54 Sb³⁺ 0.17 0.12 0.07 0.118 0.13Sum of the 99.96 100.04 99.97 100.09 100.07 components Li⁺/Si⁴⁺ 0.490.62 0.52 0.63 0.48 Σ(Li⁺, Na⁺, K⁺) 35.5 40.6 34.95 40.9 35.4 Σ(Li⁺,Na⁺, K⁺)/Si⁴⁺ 0.6 0.78 0.58 0.77 0.59 Σ(B³⁺, Al³⁺, Zn²⁺) 4.6 7.2 4.5 6.14.4 Ag⁺/Σ(Ce⁴⁺, Ce³⁺) 5.45 6 1.33 6.3 8.6

Example 1

Glass B1 was produced with a thickness of 0.5 mm in a down draw methodof the invention. By subsequent sensitization the glass was adjusted toa cooling state, which corresponds to a cooling from 500° C. to 240° C.with an average cooling rate of 80° C./h. At different positions of theglass the transmittance was measured at a wavelength of 280 nm. 40measurements were performed and the mean value of the transmittance wasat 31%. The glass was so homogeneous that the standard deviation of thetransmittance was only about 0.4% of the mean value of transmittance.

The glass was light exposed with UV-light, which had a dose of 10 J/cm²at 320 nm. For generation of through holes with a diameter of 40 μm anda distance of the hole-centers of 60 μm, the regions not to be exposedwere covered with a mask. Subsequently, the glass was tempered at atemperature of 580° C. for one hour. The etching step was done in a 10%HF-solution at room temperature. The etching ratio was 50 to 1. Throughholes with an average diameter of approximately 40 μm were obtained,wherein the standard deviation of the hole-diameter was less than 1 μm.

Example 2

The glass described in example 1 was light exposed as described inexample 1. However, the tempering temperature was varied forinvestigating its influence on the etching rate. The highest etchingratio is obtained at a tempering temperature of 580° C.

Example 3

The glass described in example 1 was processed as described inexample 1. However, the designed hole-diameter was varied. It turned outthat the standard deviation is independent from the designedhole-diameter.

Example 4

Glass B2 was produced with a thickness of 1 mm in a down draw method ofthe invention. By subsequent sensitization the glass was adjusted to acooling state, which corresponds to a cooling from 550° C. to 300° C.with a cooling rate of 40° C./h. The glass was so homogeneous that at 60measurements at a wavelength of 280 nm the standard deviation of thetransmittance was only about 0.5% of the respective transmittance value.

Example 5

A glass of the invention was divided into several pieces so that severalsamples were obtained. Some of the samples remained untreated and servedas comparative examples, while other samples were subjected to asensitization step. An increase in the transmittance at 280 nm wasdetected in the sensitized samples in comparison to the non-sensitizedcomparative examples. It was found that the increase in transmittancepositively correlated with the level of the temperature T1 duringsensitization.

Example 6

In order to determine the influence of antimony on the transmittanceproperties, two glasses of the invention were compared, which differedonly with regard to the antimony-content. This was 0.15 cat.-% and 0.2cat.-%, respectively. Transmittance was 1.2% at a wavelength of 260 nmat a 1 mm thick glass with the higher antimony-content. In contrast itwas surprisingly found that transmission at 260 nm at a 1 mm thick glasswith the lower antimony-content was 1.9%. By this increase oftransmittance in the UV-region the light exposure time required forsufficient crystallization was reduced from 14 minutes in the glass withthe higher antimony-content to 5 minutes in the glass with the lowerantimony-content. At thicker glasses there was also an increase in theachievable structure depth from 1.7 mm in the glass with highantimony-content to 3 mm in the glass with the lower antimony-content.

Example 7

A glass of the invention was light exposed with an IR-femtosecond laserwith a wavelength of 960 nm. The dose was 0.2 J/cm². The glass was sohomogeneous that a focusing was possible in a depth of 20 mm. After 90minutes of etching glass bodies with two entrance openings with adiameter of 500 μm and a depth of 20 mm each were obtained, which wereconnected by a channel with a diameter of 100 μm, which extended in adepth of 20 mm from one entrance-hole to the other entrance-hole.

FIG. 1 shows the cooling curve of glass B1.

FIG. 2 shows a cooling curve with logarithmically plotted x-axis.

FIG. 3 shows the influence of sensitization of an example glass on thetransmittance in the UV-region. Transmittance at 280 nm was measured ata sample thickness of 1 mm. The relative increase in transmittance isshown for the sensitized samples A to C in comparison to anon-sensitized comparative sample. Samples A to C differ with regard tothe temperature during sensitization. Temperature T1 was lower in sampleA than in sample B and in sample B lower than in sample C. It is evidentthat the increase in transmittance at 280 nm is more pronounced withincreasing temperature T1.

FIG. 4 shows transmittance of an example glass with a thickness of 1 mmin dependence from the wavelength.

FIG. 5 shows the dependence of the achieved etching ratio from thetempering temperature. On the x-axis the tempering temperature and onthe y-axis the achieved etching ratio is shown. The highest etchingratio is obtained at a tempering temperature of 580° C.

FIG. 6 shows the standard deviation of the obtained hole-diameter independence from the designed hole-diameter. The standard deviations areshown both for the top side (diamonds) and the down side (squares) ofthe through holes. The standard deviation (in μm) is shown on they-axis. The designed hole-diameter is shown on the x-axis. The resultsshow that the standard deviation is independent of the designedhole-diameter.

What is claimed is:
 1. A sensitized, photo-structurable glass,comprising: Si⁴⁺, a crystal-agonist, a crystal-antagonist, and a pair ofnucleating agents, wherein the crystal-agonist is selected from thegroup consisting of Na⁺, K⁺, Li⁺, and any combinations thereof, whereinthe crystal-antagonist is selected from the group consisting of Al³⁺,B³⁺, Zn²⁺, Sn²⁺, Sb³⁺, and any combinations thereof, wherein the pair ofnucleating agents comprises cerium and an agent selected from the groupconsisting of silver, gold, copper, and any combinations thereof,wherein the crystal-agonists have a molar proportion in cat.-% inrelation to a molar proportion of Si⁴⁺ of at least 0.3 and at most 0.85,and wherein the glass has a cooling state that corresponds to a steadycooling from a first temperature to a second temperature with a coolingrate of at most 200° C./h, the first temperature being at least above aglass transition temperature of the glass and the second temperature isat least 150° C. below the first temperature.
 2. The glass according toclaim 1, further comprising the following components in cat.-%: Si⁴⁺ 45to 65, Crystal-agonists 30 to 45, and Crystal-antagonists 3.5 to
 9.  


3. The glass according to claim 1, further comprising the followingcomponents in cat.-%: Si⁴⁺ 45 to 65 Crystal-agonists Li⁺ 25 to 40 K⁺ 0to 8 Na⁺ 0 to 8 Crystal-antagonists B³⁺ 0 to 5 Al³⁺  0 to 10 Zn²⁺ 0 to 4Sb³⁺  0 to 0.4 Nucleating agents Ce³⁺/Ce⁴⁺  >0 to 0.3 Ag⁺  >0 to 0.5.


4. The glass according to claim 1, further comprising contains between0.02 and 0.2 cat.-% Sb³⁺.
 5. The glass according to claim 1, furthercomprising a transmittance value that is at least 8% at a glassthickness of 1 mm and a wavelength of 280 nm.
 6. The glass according toclaim 1, further comprising an internal transmittance of at most 50% at314 nm and at a thickness of 1 mm.
 7. The glass according to claim 1,further comprising a surface having a roughness of less than 5 nm.
 8. Acrystallized product obtainable by light exposure and tempering of aglass according to claim
 1. 9. The crystallized product according toclaim 8, comprising a depth of light exposure of at least 1 mm.
 10. Astructured product obtainable by light exposure, tempering andstructuring of a glass according to claim
 1. 11. The structured productaccording to claim 10, wherein the structured product is suitable for ause selected from the group selected consisting of a micro-technologycomponent, a micro-reaction-technology component, an electronicpackaging component, a micro-fluidic component, an FED spacer, abio-technology component, an interposer, and a three-dimensionalstructured antennae.
 12. A method for producing a sensitized,photo-structurable glass, comprising: mixing raw materials to obtain amixture; melting the mixture to obtain a melt comprising Si⁴⁺, acrystal-agonist, a crystal-antagonist, and a pair of nucleating agents,wherein the crystal-agonist is selected from the group consisting ofNa⁺, K⁺, Li⁺, and any combinations thereof, wherein thecrystal-antagonist is selected from the group consisting of Al³⁺, B³⁺,Zn²⁺, Sn²⁺, Sb³⁺, and any combinations thereof, wherein the pair ofnucleating agents comprises cerium and an agent selected from the groupconsisting of silver, gold, copper, and any combinations thereof,wherein the crystal-agonists have a molar proportion in cat.-% inrelation to a molar proportion of Si⁴⁺ of at least 0.3 and at most 0.85;and solidifying the melt.
 13. The method according to claim 12, whereinthe step of solidifying the melt comprises cooling the melt from a firsttemperature to a second temperature with an average cooling rate of atmost 200° C./h.
 14. The method according to claim 13, wherein the firsttemperature is at least above a glass transition temperature of theglass and the second temperature is at least 150° C. below the firsttemperature.
 15. The method according to claim 12, further comprisingsensitizing the glass subsequent to solidifying the melt, thesensitizing step comprises re-heating the melt, then cooling there-heated melt from a first temperature to a second temperature with anaverage cooling rate of at most 200° C./h.
 16. The method according toclaim 15, wherein the first temperature is at least above a glasstransition temperature of the glass and the second temperature is atleast 150° C. below the first temperature.